Functional dependency

Updated April 02, A functional dependency in a database enforces a set of constraints between attributes.

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Functional dependency example, by A. Since the values of A are unique a1, a2, a3, etc.

Trivial functional dependency

Equation for axiom of augmentation. This occurs when one attribute in a relation uniquely determines another attribute. Functional dependency example, by A. Figure We might have a table Employee with attributes employee, title, department, location and manager. Here are a few examples. Continue Reading. This must also work for a composite PK. Given SIN, we can determine any of the other attributes within the table. For any relation R, attribute Y is functionally dependent on attribute X usually the PK , if for every valid instance of X, that value of X uniquely determines the value of Y. For example, if:. Looking at actual data can help clarify which attributes are dependent and which are determinants. The left side of a functional dependency can include more than one attribute. Table

Without normalization, there is no assurance that the data in a database is accurate and dependable. As you look at this table, ask yourself: What kind of dependencies can we observe among the attributes in Table R?

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Equation for axiom of transitivity. Here are a few examples. The attribute SSN will determine the value of name, date of birth, address and perhaps other values, because a social security number is unique, while a name, date of birth or address may not be.

The table below has information not directly related to the student; for instance, ProgramID and ProgramName should have a table of its own.

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Put another, more concrete way, if we know the value of the SSN attribute, we can find the value of name, date of birth and address.

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Functional Dependency in DBMS